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Abstract
In this study the use of a nm thick plasma polymerised primer layer as a means of enhancing the adhesion of silicone elastomer to stainless steel was investigated. This primer layer was formed from tetraethoxysilane (TEOS) and polyhydrogenmethyl siloxane (PHMS). This primer mixture was nebulized into helium atmospheric pressure plasma formed using the PlasmaStream™ system. The resulting primer coatings were characterised using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, optical profilometry, scanning electron microscopy, spectroscopic ellipsometry and water contact angle measurements. The adhesion of the silicone elastomer was accessed using 45° peel strength measurements. This study investigated the effect of plasma jet to substrate distance on primer performance. Increased coating oxidation is observed as this gap between the jet orifice and substrate increases. The plasma power, measured using current and voltage probes was observed to increase with gap height. The corresponding coating thickness decreased from 450 to 100 nm as the gap height increased from 2 to 12 mm. Associated with this change there was a 38% reduction in silicone elastomer adhesion to the stainless steel surface, demonstrating that silicone elastomer bonded to the thinner and less oxidised primer layer exhibited superior adhesion.
